This invention relates to a centrifugal pump, specifically, to a seal mechanism provided between an impeller of a pump and a casing defining a pump chamber around the impeller for receiving a fluid discharged from the impeller to prevent fluid from leaking from the pump chamber through a space formed between the casing and the impeller.
FIG. 8 shows such a prior art seal mechanism including an annular seal member 10 fixedly provided on a casing 14 for defining a pump chamber 16 around an impeller 12 for receiving fluid discharged from the impeller in such a manner that the annular seal member 10 blocks an annular space 18 formed between the casing and the impeller leaving an annular small gap 20.
In the seal mechanism, it is necessary for the annular gap 20 between the seal member 10 and the impeller 12 to be maintained appropriately. If the gap is large, an undesirable amount fluid leakage from the pump chamber will occur. To the contrary, if the gap is too small, the impeller is liable to contact with the seal member, thereby causing problems such as overload and noise. However, it is difficult for the annular seal member to be positioned properly relative to the impeller 12 which cooperates with the seal member to define the gap 20 and further it is difficult for the gap to be maintained appropriately as the size of the gap readily varies due to changes in the relative position between the casing and the impeller or a displacement of those elements.